U.S. patent number 10,222,281 [Application Number 15/128,453] was granted by the patent office on 2019-03-05 for force detection apparatus having high sensor sensitivity.
This patent grant is currently assigned to DENSO CORPORATION. The grantee listed for this patent is DENSO CORPORATION. Invention is credited to Shoji Hashimoto, Takashi Katsumata, Kentaro Mizuno, Yoshie Ohira, Rie Taguchi, Kouhei Yamaguchi.
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United States Patent |
10,222,281 |
Mizuno , et al. |
March 5, 2019 |
Force detection apparatus having high sensor sensitivity
Abstract
A force detection apparatus includes a substrate and a force
transmission block. The substrate includes: a high-sensitive mesa
gauge that is provided on a main surface, extends in a first
direction to produce a relatively large change of an electric
resistance in accordance with compressive stress, and includes a
top surface; a low-sensitive mesa gauge that is provided on the
main surface, extends in a second direction to produce a relatively
small change of an electric resistance, and includes a top surface;
and a mesa lead that is provided on the main surface, extends in a
third direction, and includes a top surface. The force transmission
block contacts the top surface of the high-sensitive mesa gauge and
the top surface of the low-sensitive mesa gauge, and is non-contact
with at least a part of the top surface of the mesa lead.
Inventors: |
Mizuno; Kentaro (Nagakute,
JP), Taguchi; Rie (Nagakute, JP),
Hashimoto; Shoji (Nagakute, JP), Ohira; Yoshie
(Nagakute, JP), Katsumata; Takashi (Kariya,
JP), Yamaguchi; Kouhei (Kariya, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO CORPORATION |
Kariya, Aichi-pref. |
N/A |
JP |
|
|
Assignee: |
DENSO CORPORATION (Kariya,
JP)
|
Family
ID: |
57348130 |
Appl.
No.: |
15/128,453 |
Filed: |
March 24, 2015 |
PCT
Filed: |
March 24, 2015 |
PCT No.: |
PCT/JP2015/001670 |
371(c)(1),(2),(4) Date: |
September 23, 2016 |
PCT
Pub. No.: |
WO2015/146154 |
PCT
Pub. Date: |
October 01, 2015 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20170102274 A1 |
Apr 13, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Mar 26, 2014 [JP] |
|
|
2014-063198 |
Jun 12, 2014 [JP] |
|
|
2014-121824 |
Mar 9, 2015 [JP] |
|
|
2015-045682 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01L
1/18 (20130101); G01L 9/0055 (20130101); G01L
9/06 (20130101); G01L 9/0054 (20130101) |
Current International
Class: |
G01L
1/18 (20060101); G01L 9/06 (20060101); G01L
9/00 (20060101) |
Field of
Search: |
;73/862.627 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
2001-304997 |
|
Oct 2001 |
|
JP |
|
2004-132811 |
|
Apr 2004 |
|
JP |
|
2006-058266 |
|
Mar 2006 |
|
JP |
|
2007-263766 |
|
Oct 2007 |
|
JP |
|
Primary Examiner: Dunlap; Jonathan
Assistant Examiner: Hollington; Octavia
Attorney, Agent or Firm: Posz Law Group, PLC
Claims
The invention claimed is:
1. A force detection apparatus comprising: a substrate including a
main surface; and a force transmission block, wherein: the
substrate includes a high-sensitive mesa gauge that is provided on
the main surface, extends in a first direction to produce a
relatively large change of an electric resistance in accordance
with compressive stress, and includes a top surface, a
low-sensitive mesa gauge that is provided on the main surface,
extends in a second direction to produce a relatively small change
of an electric resistance in accordance with compressive stress,
and includes a top surface, and a mesa lead that is provided on the
main surface, extends in a third direction from a connection
portion connecting the high-sensitive mesa gauge and the
low-sensitive mesa gauge, and includes a top surface; the force
transmission block contacts the top surface of the high-sensitive
mesa gauge and the top surface of the low-sensitive mesa gauge, and
is in non-contact with at least a part of the top surface of the
mesa lead; and an area of contact between the force transmission
block and the top surface of the high-sensitive mesa gauge is
larger than an area of contact between the force transmission block
and the low-sensitive mesa gauge.
2. The force detection apparatus according to claim 1, wherein: the
force transmission block is in non-contact with all the top surface
of the mesa lead.
3. The force detection apparatus according to claim 1, wherein: the
force transmission block includes a plurality of plurality parts
disposed away from each other in the second direction; and each of
the plurality parts contacts the top surface of the low-sensitive
mesa gauge.
4. The force detection apparatus according to claim 3, wherein: the
low-sensitive mesa gauge includes a central region extending in the
second direction near a center of the low-sensitive mesa gauge, and
a peripheral region extending in the second direction from the
connection portion toward the central region; and an area of
contact between the plurality parts and the central region is
larger than an area of contact between the plurality parts and the
peripheral region.
5. The force detection apparatus according to claim 4, wherein: the
low-sensitive mesa gauge includes a central region extending in the
second direction near a center of the low-sensitive mesa gauge, and
a peripheral region extending in the second direction from the
connection portion toward the central region; and the plurality
parts that are disposed in correspondence with the central region
are provided at shorter intervals than intervals of the plurality
parts disposed in correspondence with the peripheral region.
6. A force detection apparatus comprising: a substrate including a
main surface; and a force transmission block, wherein: the
substrate includes a high-sensitive mesa gauge that is provided on
the main surface, extends in a first direction to produce a
relatively large change of an electric resistance in accordance
with compressive stress, and includes a top surface, a
low-sensitive mesa gauge that is provided on the main surface,
extends in a second direction to produce a relatively small change
of an electric resistance in accordance with compressive stress,
and includes a top surface, and a mesa lead that is provided on the
main surface, extends in a third direction from a connection
portion connecting the high-sensitive mesa gauge and the
low-sensitive mesa gauge, and includes a top surface; the force
transmission block only contacts the top surface of the
high-sensitive mesa gauge, and is in non-contact with the
low-sensitive mesa gauge; and an area of contact between the force
transmission block and the top surface of the high-sensitive mesa
gauge is larger than an area of contact between the force
transmission block and the low-sensitive mesa gauge.
7. A force detection apparatus comprising: a substrate including a
main surface; and a force transmission block, wherein: the
substrate includes a mesa gauge that is provided on the main
surface, contacts the force transmission block, and configures a
bridge circuit, a sealing portion that is provided on the main
surface and contacts the force transmission block around an entire
circumference of the mesa gauge, and a support that is provided on
the main surface, disposed in an inner area surrounded by the mesa
gauge, and contacts the force transmission block; and the support
directly contacts the force transmission block.
8. A force detection apparatus comprising: a substrate including a
main surface; a force transmission block; and a sealed space,
wherein: the substrate includes a mesa gauge that is provided on
the main surface, contacts the force transmission block, and
configures a bridge circuit, a sealing portion that is provided on
the main surface and contacts the force transmission block around
an entire circumference of the mesa gauge, and a support that is
provided on the main surface, disposed in an inner area surrounded
by the mesa gauge, and contacts the force transmission block; the
sealed space is positioned between the mesa gauge and the sealing
portion, the sealed space being airtightly separated from an
outside by the substrate and the force transmission block; and when
the force transmission block corresponding to the sealed space
bends toward the sealed space, a portion where the force
transmission block has been bended defines a point of power and the
support defines a fulcrum and the mesa gauge defines a point of
action, providing a leverage relationship.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is the U.S. national phase of International
Patent Application No. PCT/JP2015/001670 filed on Mar. 24, 2015 and
is based on Japanese Patent Application No. 2014-121824 filed on
Jun. 12, 2014, Japanese Patent Application No. 2014-63198 filed on
Mar. 26, 2014, and Japanese Patent Application No. 2015-45682 filed
on Mar. 9, 2015, the disclosures of which are incorporated herein
by reference.
TECHNICAL FIELD
The present disclosure relates to a force detection apparatus
utilizing a piezoresistance effect.
BACKGROUND ART
A force detection apparatus utilizing a piezoresistance effect has
been developed, and an example is disclosed in Patent Literature 1.
This type of force detection apparatus includes a substrate and a
force transmission block. A mesa gauge configuring a bridge circuit
is provided on a main surface of the substrate. For example, the
mesa gauge configuring the bridge circuit is disposed in
correspondence with sides of a rectangle. The mesa gauge includes a
high-sensitive mesa gauge extending in a direction to produce a
relatively large change of an electric resistance in accordance to
compressive stress, and a low-sensitive mesa gauge extending in a
direction producing a relatively small change of an electric
resistance in accordance to compressive stress. A mesa lead is
further provided on the main surface of the substrate. The mesa
lead extends from a connection portion connecting the
high-sensitive mesa gauge and the low-sensitive mesa gauge.
The force transmission block is provided so as to cover the
high-sensitive mesa gauge, the low-sensitive mesa gauge and the
mesa lead, provided on the main surface of the substrate, and to
contact a top surface of the high-sensitive mesa gauge, a top
surface of the low-sensitive mesa gauge, and a top surface of the
mesa lead. When the force transmission block presses the
high-sensitive mesa gauge, compressive stress applied to the
high-sensitive mesa gauge increases. In this case, electric
resistance of the high-sensitive mesa gauge changes by a
piezoresistance effect. Force applied to the force transmission
block is detected based on the change of the electric
resistance.
A force detection apparatus utilizing a piezoresistance effect has
been developed. This type of force detection apparatus includes a
substrate and a force transmission block. A mesa gauge configuring
a bridge circuit is provided on a main surface of the substrate.
The force transmission block contacts a top surface of the mesa
gauge. When the force transmission block presses the mesa gauge,
compressive stress applied to the mesa gauge increases. In this
case, electric resistance of the mesa gauge changes by a
piezoresistance effect. Force applied to the force transmission
block is detected based on the change of the electric
resistance.
Each of Patent Literature 2 and Patent Literature 3 discloses a
sealed force detection apparatus. The sealed force detection
apparatus is characterized by a configuration of a force
transmission block connected to a main surface of a substrate
around the entire circumference of a mesa gauge.
PRIOR ART LITERATURES
Patent Literatures
Patent Literature 1: JP 2001-304997 A
Patent Literature 2: JP 2004-132811 A
Patent Literature 3: JP 2006-058266 A
SUMMARY OF INVENTION
The inventors of the present application have found the following
regarding a force detection apparatus.
Improvement of sensor sensitivity is desired for this type of force
detection apparatus. It is an object of the present disclosure is
to provide a technology to improve sensor sensitivity of a force
detection apparatus.
The inventors of the present application have also found the
following regarding a force detection apparatus.
When a sealed force detection apparatus becomes compact, a pressure
receiving area of a force transmission block included in the sealed
force detection apparatus decreases. In this case, compressive
stress applied to a mesa gauge decreases accordingly. Thud sensor
sensitivity of the force detection apparatus is reduced. It is an
object of the present disclosure to provide a sealed force
detection apparatus having high sensor sensitivity.
According to a force detection apparatus of a first aspect of the
present disclosure, a force detection apparatus includes a
substrate; and a force transmission block. The substrate includes:
a high-sensitive mesa gauge that is provided on a main surface,
extends in a first direction to produce a relatively large change
of an electric resistance in accordance with compressive stress,
and includes a top surface; a low-sensitive mesa gauge that is
provided on the main surface, extends in a second direction to
produce a relatively small change of an electric resistance in
accordance with compressive stress, and includes a top surface; and
a mesa lead that is provided on the main surface, extends in a
third direction from a connection portion connecting the
high-sensitive mesa gauge and the low-sensitive mesa gauge, and
includes a top surface. The force transmission block contacts the
top surface of the high-sensitive mesa gauge and the top surface of
the low-sensitive mesa gauge, and is non-contact with at least a
part of the top surface of the mesa lead.
According to a force detection apparatus of another aspect of the
present disclosure, a force detection apparatus includes a
substrate, and a force transmission block. The substrate includes:
a high-sensitive mesa gauge that is provided on a main surface,
extends in a first direction to produce a relatively large change
of an electric resistance in accordance with compressive stress,
and includes a top surface; a low-sensitive mesa gauge that is
provided on the main surface, extends in a second direction to
produce a relatively small change of an electric resistance in
accordance with compressive stress, and includes a top surface; and
a mesa lead that is provided on the main surface, extends in a
third direction from a connection portion connecting the
high-sensitive mesa gauge and the low-sensitive mesa gauge, and
includes a top surface. The force transmission block only contacts
the top surface of the high-sensitive mesa gauge, and is
non-contact with the low-sensitive mesa gauge.
According to the force detection apparatus in the present
embodiment, the force transmission block does not contact at least
a part of the top surface of the mesa lead. Thus force received by
the force transmission block is efficiently transmitted to the
high-sensitive mesa gauge. Accordingly, it may be possible to
improve sensor sensitivity of the force detection apparatus.
According to a force detection apparatus of a second aspect of the
present disclosure, a force detection apparatus includes a
substrate; and a force transmission block. The substrate includes:
a mesa gauge that is provided on a main surface, contacts the force
transmission block, and configures a bridge circuit; a sealing
portion that is provided on the main surface and contacts the force
transmission block around an entire circumference of the mesa
gauge; and a support that is provided on the main surface, disposed
in an inner area surrounded by the mesa gauge, and contacts the
force transmission block.
According to the force detection apparatus in the present
embodiment, the sealed space is formed between the substrate and
the force transmission block. When force applied to the force
transmission block increases, the force transmission block bends
within the sealed space toward the substrate side. In this case, a
leverage relationship which defines the bended and deformed portion
of the force transmission block as the point of power, the support
as the fulcrum, and the mesa gauge as the point of action is
satisfied. In this case, since compressive stress applied to the
mesa gauge becomes large based on the leverage relationship
defining the mesa gauge as the point of action, it may be possible
to improve sensor sensitivity of the force detection apparatus.
BRIEF DESCRIPTION OF DRAWINGS
The above and other aspects, features and advantages of the present
disclosure will become more apparent from the following detailed
description made with reference to the accompanying drawings. In
the drawings:
FIG. 1 is a diagram illustrating a schematic cross-sectional view
of a force detection apparatus according to an example, taken along
a line I-I in FIG. 3;
FIG. 2 is a diagram illustrating a schematic cross-sectional view
of the force detection apparatus according to the example, taken
along a line II-II in FIG. 3;
FIG. 3 is a diagram illustrating a schematic plan view of a
substrate of the force detection apparatus according to the
example, illustrating with a broken line a range of contact with a
force transmission block;
FIG. 4 is a diagram illustrating the force detection apparatus
according to the example, schematically illustrating a positional
relationship between a pressing portion of the force transmission
block and a mesa gauge of the substrate;
FIG. 5 is a diagram illustrating the force detection apparatus
according to a modified example, schematically illustrating a
positional relationship between a pressing portion of the force
transmission block and a mesa gauge of the substrate;
FIG. 6 is a diagram illustrating the force detection apparatus
according to a comparison example, schematically illustrating a
positional relationship between a pressing portion of the force
transmission block and a mesa gauge of the substrate;
FIG. 7 is a diagram illustrating a schematic enlarged view of a
force detection apparatus according to the comparison example,
illustrating a condition of a high-sensitive mesa gauge when a
force transmission block receives a pressure;
FIG. 8 is a diagram illustrating the force detection apparatus
according to the modified example, schematically illustrating a
positional relationship between the pressing portion of the force
transmission block and the mesa gauge of the substrate;
FIG. 9 is a diagram illustrating the force detection apparatus
according to the modified example, schematically illustrating a
positional relationship between the pressing portion of the force
transmission block and the mesa gauge of the substrate;
FIG. 10 is a diagram illustrating the force detection apparatus
according to the modified example, schematically illustrating a
positional relationship between the pressing portion of the force
transmission block and the mesa gauge of the substrate;
FIG. 11 is a diagram illustrating a schematic cross-sectional view
of a force detection apparatus according to an example, taken along
a line XI-XI in FIG. 12;
FIG. 12 is a diagram illustrating a schematic plan view of a
substrate of the force detection apparatus according to the
example;
FIG. 13 is a diagram illustrating an enlarged cross-sectional view
of the force detection apparatus according to the example,
illustrating a main part in the vicinity of a sealed space, and
explaining leverage operation;
FIG. 14 is a diagram illustrating a schematic cross-sectional view
of the force detection apparatus according to a modified example,
corresponding to FIG. 11; and
FIG. 15 is a diagram illustrating a schematic cross-sectional view
of the force detection apparatus according to a modified example,
corresponding to FIG. 11.
PREFERRED EMBODIMENTS FOR CARRYING OUT INVENTION
A feature of a technology disclosed in this description will be
hereinafter sequentially described. Each of matters described
herein produces independent technical advantages.
(First Embodiment)
One embodiment of a force detection apparatus disclosed in the
present description is a sensor for detecting various types of
pressures. A detection target may be an air pressure or a liquid
pressure, for example. The force detection apparatus may include a
substrate and a force transmission block. It is preferable that the
substrate is made of material which changes an electric resistance
in accordance with compressive stress by a piezoresistance effect.
For example, the substrate may be provided by a semiconductor
substrate or an SOI substrate. The substrate may include a
high-sensitive mesa gauge, a low-sensitive mesa gauge, and a mesa
lead. The high-sensitive mesa gauge is provided on a main surface
of the substrate, and includes a top surface. The high-sensitive
mesa gauge extends in a first direction to produce a relatively
large change of an electric resistance in accordance with
compressive stress. The low-sensitive mesa gauge is provided on the
main surface of the substrate, and includes a top surface. The
low-sensitive mesa gauge extends in a second direction to produce a
relatively small change of an electric resistance in accordance
with compressive stress. The first direction and the second
direction cross each other. In a typical example, the
high-sensitive mesa gauge and the low-sensitive mesa gauge may form
a bridge circuit. In this case, a pair of the high-sensitive mesa
gauges may be disposed in correspondence with an opposed pair of
sides of a rectangle, while a pair of the low-sensitive mesa gauges
may be disposed in correspondence with the other opposed pair of
sides of the rectangle. The term "relatively" in this context
expresses a condition of comparison between the high-sensitive mesa
gauge and the low-sensitive mesa gauge. In other words, an electric
resistance of the high-sensitive mesa gauge produces a larger
change in accordance with compressive stress than an electric
resistance of the low-sensitive mesa gauge. The mesa lead is
provided on the main surface of the substrate, and includes a top
surface. The mesa lead extends in a third direction from a
connection portion connecting the high-sensitive mesa gauge and the
low-sensitive mesa gauge. The third direction may cross both the
first direction and the second direction, or extend in parallel
with either one of the first direction and the second direction.
The force transmission block contacts the top surface of the
high-sensitive mesa gauge and the top surface of the low-sensitive
mesa gauge. The force transmission block does not contact at least
a part of the top surface of the mesa lead. In other words, the
force transmission block is brought into a non-contact state at
least from a part of the top surface of the mesa lead. It is
preferable that the force transmission block does not contact the
top surface of the mesa lead.
According to the force detection apparatus of this embodiment, the
contact area of the force transmission block to the top surface of
the high-sensitive mesa gauge may be larger than the contact area
of the force transmission block to the top surface of the
low-sensitive mesa gauge. In this force detection apparatus, since
the contact area of the force transmission block to the
high-sensitive mesa gauge are different from the contact area of
the force transmission block to the low-sensitive mesa gauge, a
large quantity of force received by the force transmission block
can be transmitted to the high-sensitive mesa gauge. According to
this structure, compressive stress applied to the high-sensitive
mesa gauge increases, and therefore sensor sensitivity of the force
detection apparatus improves. There may be a configuration which
only allows contact between the force transmission block and the
top surface of the high-sensitive mesa gauge in order to increase
sensor sensitivity of the force detection apparatus. However, in
the force detection apparatus having this configuration, the force
transmission block is not supported by the low-sensitive mesa
gauge. When the force transmission block bends toward the substrate
side, the high-sensitive mesa gauge deforms one-sidedly, so that
linearity between compressive stress and electric resistances may
deteriorate. When the force transmission block contacts both the
top surface of the high-sensitive mesa gauge and the top surface of
the low-sensitive mesa gauge, the bend of the force transmission
block and the one-sided deformation of the high-sensitive mesa
gauge decrease. Accordingly, linearity between compressive force
and electric resistances improves. According to the force detection
apparatus of this embodiment, sensor sensitivity and linearity both
may improve.
According to the force detection apparatus of this embodiment, the
force transmission block may include multiple plurality parts
disposed away from each other in the second direction. In this
case, each of the plurality parts may contact the top surface of
the low-sensitive mesa gauge. According to the force detection
apparatus of this embodiment, a bend of the force transmission
block decreases, and therefore both the sensor sensitivity and the
linearity improve.
The low-sensitive mesa gauge may include a central region extending
in the second direction in the vicinity of the center of the
low-sensitive mesa gauge, and a peripheral region extending in the
second direction from the connection portion toward the central
region. According to the force detection apparatus including
multiple plurality parts in the force transmission block, each of
which plurality parts contacts the top surface of the low-sensitive
mesa gauge, an area contacting between the plurality parts and the
central region may be larger than an area of contact between the
plurality parts and the peripheral region. According to the force
detection apparatus of this embodiment, it may be possible to
effectively reduce the bend of the force transmission block while
decreasing the contact area between the force transmission block
and the low-sensitive mesa gauge. Accordingly, sensor sensitivity
and linearity of the force detection apparatus of this embodiment
further improves.
The low-sensitive mesa gauge may include a central region extending
in the second direction in the vicinity of the center of the
low-sensitive mesa gauge, and a peripheral region extending in the
second direction from the connection portion toward the central
region. According to the force detection apparatus including the
plurality parts in the force transmission block, each of which
plurality parts contacts the top surface of the low-sensitive mesa
gauge, the plurality parts disposed in correspondence with the
central region may be provided more densely than the plurality
parts disposed in correspondence with the peripheral region.
According to the force detection apparatus of this embodiment, it
may be possible to effectively reduce the bend of the force
transmission block while decreasing the contact area between the
force transmission block and the low-sensitive mesa gauge.
Accordingly, both sensor sensitivity and linearity of the force
detection apparatus of this embodiment further improves.
(First Example)
As illustrated in FIG. 1 to FIG. 3, a force detection apparatus 1
is, for example, a semiconductor pressure sensor detecting a vessel
internal pressure of a pressure vessel. The force detection
apparatus 1 includes a semiconductor substrate 2 and a force
transmission block 4.
As illustrated in FIG. 1 and FIG. 2, the semiconductor substrate 2
is made of n-type single crystal silicon, including a main surface
2S constituted by a (110) crystal surface. Multiple grooves 11 are
formed in the main surface 2S of the semiconductor substrate 2. The
multiple grooves 11 define a detection portion 10 in the main
surface 2S of the semiconductor substrate 2.
As illustrated in FIG. 3, the detection portion 10 includes mesa
gauges 12, 14, 16, and 18 configuring a bridge circuit. As
illustrated in FIG. 1 and FIG. 2, each of the mesa gauges 12, 14,
16, and 18 protrudes in a mesa shape from the bottom of the
corresponding groove 11. Each height of the mesa gauges 12, 14, 16,
and 18 ranges approximately from 0.5 .mu.m to 5 .mu.m. Each top
surface of the mesa gauges 12, 14, 16, and 18 is flush with the
main surface 2S of the semiconductor substrate 2 around the grooves
11. More specifically, the mesa gauges 12, 14, 16, and 18
correspond to remaining parts after the multiple grooves 11 are
formed in the main surface 2S of the semiconductor substrate 2 by
dry etching, for example.
As illustrated in FIG. 3, the mesa gauges 12, 14, 16, and 18 of the
detection portion 10 are disposed in correspondence with sides of a
square. The mesa gauges 14 and 18 configuring an opposed pair of
the sides are referred to as the first high-sensitive mesa gauge 14
and the second high-sensitive mesa gauge 18, respectively. The mesa
gauges 12 and 16 configuring the other opposed pair of the sides
are referred to as the first low-sensitive mesa gauge 12 and the
second low-sensitive mesa gauge 16, respectively.
The first high-sensitive mesa gauge 14 and the second
high-sensitive mesa gauge 18 extend in a <110> direction of
the semiconductor substrate 2. Each of the first high-sensitive
mesa gauge 14 and the second high-sensitive mesa gauge 18 extending
in the <110> direction of the semiconductor substrate 2 is
characterized by producing a large change of an electric resistance
in accordance with compressive stress, i.e., a component exhibiting
a piezoresistance effect.
The first low-sensitive mesa gauge 12 and the second low-sensitive
mesa gauge 16 extends in a <100> direction of the second
semiconductor substrate 2. Each of the first low-sensitive mesa
gauge 12 and the second low-sensitive mesa gauge 16 extending in
the <100> direction of the semiconductor substrate 2 is
characterized by producing substantially no change of an electric
resistance in accordance with compressive stress, that is, a
component exhibiting substantially no piezoresistance effect.
As illustrated in FIG. 1 and FIG. 2, gauge portions 12a, 14a, 16a,
and 18a, each of which contains p-type impurities, are formed on
the surfaces of the mesa gauges 12, 14, 16, and 18, respectively.
Each impurity concentration of the gauge portions 12a, 14a, 16a,
and 18a is approximately in a range from 1.times.10.sup.18
cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3. The gauge portions 12a,
14a, 16a, and 18a are brought into a substantially insulated state
from the n-type semiconductor substrate 2 by pn junction.
As illustrated in FIG. 3, wiring portions 22, 24, 26, and 28, each
of which contains p-type impurities, are disposed on the main
surface 2S of the semiconductor substrate 2. Each impurity
concentration of the wiring portions 22, 24, 26, and 28 is
approximately in a range from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.21 cm.sup.-3. The wiring portions 22, 24, 26, and 28
electrically connect the detection portion 10 and electrodes 32,
34, 36, and 38, respectively. The electrodes 32, 34, 36, and 38 are
provided on the main surface 2S of the semiconductor substrate 2,
and disposed on an area out of a range covered by the force
transmission block 4.
One end of the first wiring portion 22 is connected with a first
connection portion 13 connecting the gauge portion 12a of the first
low-sensitive mesa gauge 12 and the gauge portion 14a of the first
high-sensitive mesa gauge 14. The other end of the first wiring
portion 22 is connected with the first electrode 32. The first
wiring portion 22 includes a first mesa lead 22a on the first
connection portion 13 side of the mesa gauges 12 and 14. The first
mesa lead 22a protrudes in a mesa shape from the bottom of the
corresponding groove 11. The first mesa lead 22a is produced in the
same step as the manufacturing step of the mesa gauges 12, 14, 16,
and 18.
One end of the second wiring portion 24 is connected with a second
connection portion 15 connecting the gauge portion 14a of the first
high-sensitive mesa gauge 14 and the gauge portion 16a of the
second high-sensitive mesa gauge 16. The other end of the second
wiring portion 24 is connected with the second electrode 34. The
second wiring portion 24 includes a second mesa lead 24a on the
second connection portion 15 side of the mesa gauges 14 and 16. The
second mesa lead 24a protrudes in a mesa shape from the bottom of
the corresponding groove 11. The second mesa lead 24a is produced
in the same step as the manufacturing step of the mesa gauges 12,
14, 16, and 18.
One end of the third wiring portion 26 is connected with a third
connection portion 17 connecting the gauge portion 16a of the
second low-sensitive mesa gauge 16 and the gauge portion 18a of the
second high-sensitive mesa gauge 18. The other end of the third
wiring portion 26 is connected with the third electrode 36. The
third wiring portion 26 includes a third mesa lead 26a on the third
connection portion 17 side of the mesa gauges 16 and 18. The third
mesa lead 26a protrudes in a mesa shape from the bottom of the
corresponding groove 11. The third mesa lead 26a is produced in the
same step as the manufacturing step of the mesa gauges 12, 14, 16,
and 18.
One end of the fourth wiring portion 28 is connected with a fourth
connection portion 19 connecting the gauge portion 18a of the
second high-sensitive mesa gauge 18 and the gauge portion 12a of
the first low-sensitive mesa gauge 12. The other end of the fourth
wiring portion 28 is connected with the fourth electrode 38. The
fourth wiring portion 26 includes a fourth mesa lead 28a on the
fourth connection portion 19 side of the mesa gauges 12 and 18. The
fourth mesa lead 28a protrudes in a mesa shape from the bottom of
the corresponding groove 11. The fourth mesa lead 28a is produced
in the same step as the manufacturing step of the mesa gauges 12,
14, 16, and 18.
As illustrated in FIG. 1 and FIG. 2, the force transmission block 4
has a rectangular parallelepiped shape, and includes a silicon
layer 4a and a silicon oxide layer 4b. The semiconductor substrate
2 and the force transmission block 4 are connected with each other
by cold-solid phase welding. More specifically, the main surface 2S
of the semiconductor substrate 2 and the surface of the silicon
oxide layer 4b of the force transmission block 4 are activated by
using argon ions. Thereafter, the main surface 2S of the
semiconductor substrate 2 and the surface of the silicon oxide
layer 4b of the force transmission block 4 are brought into contact
with each other in ultra-high vacuum to connect both the
surfaces.
As illustrated in FIG. 1 and FIG. 2, a part of the silicon oxide
layer 4b in the force transmission block 4 is removed to form a
groove 4c on a surface of the force transmission block 4 on the
semiconductor substrate 2 side. The groove 4c thus formed divides
the silicon oxide layer 4b of the force transmission block 4 into a
sealing portion 40a and a pressing portion 40b. In addition, the
groove 4c thus formed produces a sealed space 6 between the
semiconductor substrate 2 and the force transmission block 4 as a
space separated from the outside.
The sealing portion 40a of the force transmission block 4 is
connected to the main surface 2S of the semiconductor substrate 2
around the entire circumference of the mesa gauges 12, 14, 16, and
18. The semiconductor substrate 2 includes a sealing portion 20 to
which the sealing portion 40a is connected. The sealing portion 20
of the semiconductor substrate 2 and the sealing portion 40a of the
force transmission block 4 are airtightly connected with each
other.
FIG. 4 illustrates a positional relationship between the pressing
portion 40b of the force transmission block 4 and the mesa gauges
12, 14, 16, and 18. The pressing portion 40b has a point
symmetrical shape, and connects with a part of each top surface of
the mesa gauges 12, 14, 16, and 18. The pressing portion 40b
connects a major part of each top surface of the high-sensitive
mesa gauges 14 and 18. The pressing portion 40b does not contact
ends of each top surface of the high-sensitive mesa gauges 14 and
18 (top surface in the vicinity of the connection portions 13, 15,
17, and 19). The pressing portion 40b connects a major part of each
top surface of the low-sensitive mesa gauges 12 and 16. The
pressing portion 40b does not contact either ends of each top
surface of the low-sensitive mesa gauges 12 and 16 (top surface in
the vicinity of the connection portions 13, 15, 17, and 19). The
pressing portion 40b does not contact each top surface of the mesa
leads 22a, 24a, 26a, and 28a, and does not contact each top surface
of the connection portions 13, 15, 17, and 19.
Operation of the force detection apparatus 1 will be hereinafter
described. Initially, the force detection apparatus 1 during the
use is brought into a state of connection between the first
electrode 32 and a constant current source, grounding of the third
electrode 36, and connection of a voltmeter between the second
electrode 34 and the fourth electrode 38. In the force detection
apparatus 1, compressive stress applied to the gauge portions 12a,
14a, 16a, and 18a of the mesa gauges 12, 14, 16, and 18 via the
force transmission block 4 changes when a vessel internal pressure
applied to the force transmission block 4 changes. Electric
resistances of the gauge portions 14a and 18a of the high-sensitive
mesa gauges 14 and 18 change in proportion to the compressive
stress by the piezoresistance effect of the high-sensitive mesa
gauges 14 and 18. In this case, a potential difference between the
second electrode 34 and the fourth electrode 38 becomes
proportional to the compressive stress applied to the gauge
portions 14a and 18a. Accordingly, the vessel internal pressure
applied to the force transmission block 4 is detectable based on a
voltage change measured by the voltmeter.
In the force detection apparatus 1, the pressing portion 40b of the
force transmission block 4 does not contact each top surface of the
mesa leads 22a, 24a, 26a, and 28a. In this case, the vessel
internal pressure applied to the force transmission block 4 is
efficiently transmitted to the high-sensitive mesa gauges 14 and
18. Accordingly, sensor sensitivity of the force detection
apparatus 1 improves.
According to the force detection apparatus 1 of this type, a
voltage drop produced by parasitic resistances of the mesa leads
22a, 24a, 26a, and 28a deteriorates sensor sensitivity.
Accordingly, it is preferable that the widths of the mesa leads
22a, 24a, 26a, and 28a of the force detection apparatus 1 (widths
in directions parallel with the main surface 2S of the
semiconductor substrate 2 and perpendicular to longitudinal
directions of the mesa leads 22a, 24a, 26a, and 28a) are larger
than the widths of the mesa gauges 12, 14, 16, and 18 (widths in
directions parallel with the main surface 2S of the semiconductor
substrate 2 and perpendicular to longitudinal directions of the
mesa gauges 12, 14, 16, and 18). According to this structure, the
parasitic resistances of the mesa leads 22a, 24a, 26a, and 28a
decrease, and therefore sensor sensitivity of the force detection
apparatus 1 improves.
Incidentally, in a case of a force transmission block which is in
contact with each top surface of mesa leads as in a conventional
force detection apparatus, a vessel internal pressure applied to
the force transmission block is also transmitted to the mesa leads
when the widths of the mesa leads are large. In this case,
compressive stress applied to the high-sensitive mesa gauges
decreases. Accordingly, even when parasitic resistances are reduced
by increasing the widths of the mesa leads in the conventional
force detection apparatus, sensor sensitivity is difficult to
improve due to decrease in compressive stress applied to the
high-sensitive mesa gauges. In the force detection apparatus 1 of
the present example, the force transmission block 4 does not
contact each top surface of the mesa leads 22a, 24a, 26a, and 28a.
In this case, compressive stress applied to the high-sensitive mesa
gauges 14 and 18 does not decrease even when the widths of the mesa
leads 22a, 24a, 26a, and 28a are enlarged. Accordingly, sensor
sensitivity of the force detection apparatus 1 of this example
effectively improves with the large widths of the mesa leads 22a,
24a, 26a, and 28a.
A force detection apparatus according to a modified example and a
comparison example will be hereinafter described. Configurations
common to the corresponding configurations of the force detection
apparatus 1 described above have been given common reference
numbers, and the same explanation of the configurations is not
repeated.
According to the force detection apparatus of the modified example
illustrated in FIG. 5, the pressing portion 40b of the force
transmission block has a different layout between the
high-sensitive mesa gauges 14 and 18 and the low-sensitive mesa
gauges 12 and 16. The pressing portion 40b contacts a major part of
each top surface of the high-sensitive mesa gauges 14 and 18, and
therefore the contact area between the pressing portion 40b and the
high-sensitive mesa gauges 14 and 18 is relatively large. The area
occupied by the contact part of the top surfaces of the
high-sensitive mesa gauges 14 and 18 contacting the pressing
portion 40b in the total area of the entire top surfaces of the
high-sensitive mesa gauges 14 and 18 is relatively large. The
pressing portion 40b selectively contacts a part of each top
surface of the low-sensitive mesa gauges 12 and 16 in the vicinity
of the center thereof, and therefore the contact area between the
pressing portion 40b and the low-sensitive mesa gauges 12 and 16 is
relatively small. The area occupied by the contact part of the top
surfaces of the low-sensitive mesa gauges 12 and 16 contacting the
pressing portion 40b in the total area of entire top surfaces of
the low-sensitive mesa gauges 12 and 16 is relatively small. As can
be understood, the contact area of the pressing portion 40b in
contact with each of the high-sensitive mesa gauges 14 and 18 is
different from the contact area of the pressing portion 40b in
contact with each of the low-sensitive mesa gauges 12 and 16
according to the force detection apparatus of this modified
example. In this case, a vessel internal pressure applied to the
force transmission block is efficiently transmitted to the
high-sensitive mesa gauges 14 and 18. Accordingly, sensor
sensitivity of the force detection apparatus of this modified
example improves.
In order to explain other characteristics of the force detection
apparatus of the modified example, a force detection apparatus of a
comparison example will be described. According to the force
detection apparatus of the comparison example illustrated in FIG.
6, the pressing portion 40b of the force transmission block only
contacts the pair of high-sensitive mesa gauges 14 and 18. In case
of this configuration, a vessel internal pressure applied to the
force transmission block is efficiently transmitted to the
high-sensitive mesa gauges 14 and 18.
However, when a vessel internal pressure is applied to the force
transmission block 4, an area surrounded by the mesa gauges bends
toward the semiconductor device 2 so as to have a convex shape with
the peak of the convex shape located at the center point of the
bended area as illustrated in FIG. 7. This bend of the force
transmission block 4 one-sidedly deforms the high-sensitive mesa
gauges 14 and 18 toward the inside. As a result, linearity between
compressive stress and electric resistances deteriorates.
According to the force detection apparatus of the modified example
illustrated in FIG. 5, the pressing portion 40b of the force
transmission block also contacts a part of each top surface of the
low-sensitive mesa gauges 12 and 16. This structure reduces a bend
of the force transmission block, thereby decreasing one-sided
deformation of the high-sensitive mesa gauges 14 and 18. In this
case, linearity between compressive stress and electric resistances
improves in the force detection apparatus of the modified example.
According to the force detection apparatus of the modified example,
it may be possible to both obtain sensor sensitivity and
linearity.
According to a force detection apparatus of a modified example
illustrated in FIG. 8, the pressing portion 40b of the force
transmission block includes multiple plurality parts 40c that are
located apart from each other in each longitudinal direction of the
low-sensitive mesa gauges 12 and 16. Each of the plurality parts
40c contacts the corresponding top surface of the low-sensitive
mesa gauges 12 and 16. The plurality parts 40c are disposed at
equal intervals in each longitudinal direction of the low-sensitive
mesa gauges 12 and 16. According to the force detection apparatus
of this modified example, a bend of the force transmission block 4
decreases, and therefore linearity between compressive stress and
electric resistances improves.
A force detection apparatus according to modified examples
illustrated in FIG. 9 and FIG. 10 will be hereinafter described.
For easy understanding of characteristics of the force detection
apparatus of the modified examples, each of the low-sensitive mesa
gauges 12 and 16 is divided into three regions in the longitudinal
direction in the following description as illustrated in FIG. 9 and
FIG. 10. (For simplifying the depiction, only the regions
corresponding to the first low-sensitive mesa gauge 12 are shown in
the drawings. However, this configuration is similarly applicable
to the second low-sensitive mesa gauge 16.) Each of the
low-sensitive mesa gauges 12 and 16 includes a central region 12A
and a pair of peripheral regions 12B. The central region 12A
extends in the vicinity of the center of the mesa gauge in the
longitudinal direction. Each of the pair of peripheral regions 12B
extends in the longitudinal direction from the corresponding one of
the connection portions 13, 15, 17 and 19 of the mesa gauges, and
reaches the central region 12A. The length of the central region
12A in the longitudinal direction is equivalent to the length of
each of the pair of peripheral regions 12B in the longitudinal
direction. In other words, in three equal divisions of each of the
low-sensitive mesa gauges 12 and 16 divided in the longitudinal
direction, the central region 12A corresponds to the division
positioned in the vicinity of the center, while each of the
peripheral regions 12B corresponds to the division positioned in
the periphery.
When a comparison is made between the central region 12A and the
peripheral regions 12B of the force detection apparatus of the
modified example illustrated in FIG. 9, the area of contact between
the top surface of the central region 12A and the plurality parts
40c is larger than the area of contact between the top surface of
one of the peripheral regions 12B and the plurality parts 40c. In
other words, the area occupied by the contact part of the top
surface of the central region 12A contacting the plurality parts
40c in the total area of the entire top surface of the central
region 12A is larger than the area of the contact part of the top
surface of one of the peripheral regions 12B contacting the
plurality parts 40c in the total area of the entire top surface of
one of the peripheral regions 12B. As described above, the force
transmission block bends in such a manner that the peak of the
convex shape is located at the center point of the force
transmission block when a vessel internal pressure is applied to
the force transmission block. The central region 12A of each of the
low-sensitive mesa gauges 12 and 16 is disposed close to the center
point of the force transmission block. According to this structure,
the central region 12A comes into contact with a wide area of the
force transmission block, and therefore the bend of the force
transmission block effectively decreases. In other words, this
structure effectively decreases the bend of the force transmission
block while reducing enlargement of the contact area between the
force transmission block and the low-sensitive mesa gauges 12 and
16. Accordingly, it may be possible to obtain sensor sensitivity
and linearity in the force detection apparatus of this modified
example. The plurality parts 40c corresponding to the peripheral
regions 12B may be eliminated depending on required
characteristics. This example corresponds to the force detection
apparatus of the modified example illustrated in FIG. 5.
Accordingly, the force detection apparatus of the modified example
illustrated in FIG. 5 also becomes a device capable of effectively
decreasing the bend of the force transmission block while reducing
enlargement of the contact area between the force transmission
block and the low-sensitive mesa gauges 12 and 16, that is, a
device realizing improvement of both sensor sensitivity and
linearity.
According to the force detection apparatus of the modified example
illustrated in FIG. 10, the plurality parts 40c disposed in
correspondence with the central part 12A are disposed at shorter
intervals than the intervals of the plurality parts 40c disposed in
correspondence with the peripheral regions 12B when a comparison is
made between the central region 12A and the peripheral regions 12B.
Similarly to the above example, the area occupied by the contact
part of the top surface of the central region 12A contacting the
plurality parts 40c in the total area of the entire top surface of
the central region 12A becomes larger than the area occupied by the
contact part of the one of the peripheral regions 12B contacting
the plurality parts 40c in the total area of the entire top surface
of one of the peripheral regions 12B in the force detection
apparatus of this modified example. Accordingly, the force
detection apparatus of this modified example also effectively
reduces a bend of the force transmission block, thereby improving
both sensitivity and linearity.
(Second Embodiment)
A force detection apparatus according to an embodiment disclosed in
this description is a sensor which detects an air pressure. A
detection target may be a combustion pressure, for example. The
force detection apparatus may include a substrate and a force
transmission block. It is preferable that the substrate is made of
material which changes an electric resistance in accordance with
compressive stress by a piezoresistance effect. For example, the
substrate includes a semiconductor substrate and an SOI substrate.
The substrate may include a mesa gauge, a sealing portion, and a
support. The mesa gauge may be formed on a main surface of the
substrate. The mesa gauge may contact the force transmission block,
and forms a bridge circuit. The mesa gauge may have a mesa-shaped
configuration. The top surface of the mesa gauge may contact the
force transmission block. The sealing portion may be formed on the
main surface, and contact the force transmission block around the
entire circumference of the mesa gauge. The support may be formed
on the main surface and disposed in an inner area surrounded by the
mesa gauge, and may contact the force transmission block. The
support may have a mesa-shaped configuration. The top surface of
the support may contact the force transmission block. It is
preferable that the rigidity of the support is higher than the
rigidity of the mesa gauge.
According to this embodiment, a sealed space may be defined as a
space airtightly separated from the outside by the substrate and
the force transmission block. The sealed space may be disposed
between the mesa gauge and the sealing portion, and have a
thickness sufficient for producing a bend of the force transmission
block.
The force transmission block of this embodiment may include a
groove on a surface of the substrate side. The groove may be
disposed between a portion in contact with the mesa gauge and
another portion in contact with the sealing portion. This groove
defines the sealed space.
According to this embodiment, the force transmission block may
include a silicon layer and a silicon oxide layer. The silicon
oxide layer may cover a part of the surface of the silicon layer on
the substrate side. In this case, the groove may be formed in a
non-covered area which is an area not covered by the silicon oxide
layer. The groove defining the sealed space is easily formed by
processing the silicon oxide layer in the force transmission
block.
(Second Example)
As illustrated in FIG. 11 and FIG. 12, a force detection apparatus
201 is, for example, a semiconductor pressure sensor that detects a
combustion pressure of an internal combustion engine, and includes
a semiconductor substrate 202 and a force transmission block
204.
The semiconductor substrate 202 is made of n-type single crystal
silicon, and includes a main surface 202S provided by a (110)
crystal surface. Multiple grooves 211 are formed on the main
surface 202S of the semiconductor substrate 202. The multiple
grooves 211 define a detection portion 210, a support 220, and a
sealing portion 230 on the main surface 202S of the semiconductor
substrate 202.
As illustrated in FIG. 12, the detection portion 210 includes mesa
gauges 212, 214, 216, and 218 configuring a bridge circuit. Each of
the mesa gauges 212, 214, 216, and 218 protrudes in a mesa shape
from the bottom of the corresponding groove 211. Each height of the
mesa gauges 212, 214, 216, and 218 ranges approximately from 0.5
.mu.m to 5 .mu.m. Each top surface of the mesa gauges 212, 214,
216, and 218 is flush with the main surface 202S of the
semiconductor substrate 202 around the grooves 211. More
specifically, the mesa gauges 212, 214, 216, and 218 are remaining
parts after the multiple grooves 211 are formed in the main surface
202S of the semiconductor substrate 202 by dry etching, for
example.
As illustrated in FIG. 12, the first mesa gauge 212 and the third
mesa gauge 216 of the detection portion 210 constitute an opposed
pair of sides of a rectangle, while the second mesa gauge 214 and
the fourth mesa gauge 218 constitute the other opposed pair of
sides of the rectangular shape. The first mesa gauge 212 and the
third mesa gauge 216 extend in a <110> direction of the
semiconductor substrate 202. Each of the first mesa gauge 212 and
the third mesa gauge 216 extending in the <110> direction of
the semiconductor substrate 202 exhibits a piezoresistance effect
which changes an electric resistance in accordance with compressive
stress. The second mesa gauge 214 and the fourth mesa gauge 218
extend in a <100> direction of the semiconductor substrate
202. Each of the second mesa gauge 214 and the fourth mesa gauge
218 extending in the <100> direction of the semiconductor
substrate 202 exhibits substantially no piezoresistance effect.
As illustrated in FIG. 11 and FIG. 12, gauge portions 212a, 214a,
216a, and 218a, each of which contains p-type impurities, are
formed on the surfaces of the mesa gauges 212, 214, 216, and 218,
respectively. Each impurity concentration of the gauge portions
212a, 214a, 216a, and 218a is approximately in a range from
1.times.10.sup.18 cm.sup.-3 to 1.times.10.sup.21 cm.sup.-3. The
gauge portions 212a, 214a, 216a, and 218a are brought into a
substantially insulated state from the n-type semiconductor
substrate 202 by pn junction.
As illustrated in FIG. 11 and FIG. 12, the support 220 is disposed
in an inner area surrounded by the mesa gauges 212, 214, 216, and
218. The support 220 protrudes in a mesa shape from the bottoms of
the grooves 211. The support 220 has a height approximately in a
range from 0.5 .mu.m to 5 .mu.m. The top surface of the support 220
is flush with the main surface 202S of the semiconductor substrate
202 around the grooves 211. More specifically, the support 220 is a
remaining part after the multiple grooves 211 are formed in the
main surface 202S of the semiconductor substrate 202 by dry
etching, for example. The support 220 has a configuration similar
to the rectangular shape formed by the mesa gauges 212, 214, 216,
and 218 in the plan view. The side length of the support 220 is
larger than each width of the mesa gauges 212, 214, 216, and 218
(width in direction perpendicular to longitudinal direction).
Accordingly, the rigidity of the support 220 is higher than the
rigidity of the mesa gauges 212, 214, 216, and 218.
As illustrated in FIG. 12, wiring portions 232, 234, 236, and 238,
each of which contains p-type impurities, are disposed on the main
surface 202S of the semiconductor substrate 202. Each impurity
concentration of the wiring portions 232, 234, 236, and 238 is
approximately in a range from 1.times.10.sup.18 cm.sup.-3 to
1.times.10.sup.21 cm.sup.-3. One end of the first wiring portion
232 is connected with a connection portion connecting a first gauge
portion 212a and a second gauge portion 214a. The other end of the
first wiring portion 232 is connected with a first electrode 242.
One end of the second wiring portion 234 is connected with a
connection portion connecting the second gauge portion 214a and a
third gauge portion 216a. The other end of the second wiring
portion 234 is connected with a second electrode 244. One end of
the third wiring portion 236 is connected with a connection portion
connecting the third gauge portion 216a and a fourth gauge portion
218a. The other end of the third wiring portion 236 is connected
with a third electrode 246. One end of the fourth wiring portion
238 is connected with a connection portion connecting the fourth
gauge portion 218a and the first gauge portion 212a. The other end
of the fourth wiring portion 238 is connected with a fourth
electrode 248. Each of the electrodes 242, 244, 246, and 248 is
provided on the main surface 202S of the semiconductor substrate
202, and disposed in an area out of a range covered by the force
transmission block 204.
As illustrated in FIG. 11, the force transmission block 204 has a
rectangular parallelepiped shape, and includes a silicon layer 204a
and a silicon oxide layer 204b. The silicon oxide layer 204b covers
a part of surface of the silicon layer 204a on the semiconductor
substrate 202 side. The force transmission block 204 is connected
to the main surface 202S of the semiconductor substrate 202 around
the entire circumference of the mesa gauges 212, 214, 216, and 218.
The semiconductor substrate 202 includes a sealing portion 230 to
which the force transmission block 204 is connected. The sealing
portion 230 of the semiconductor substrate 202 and the force
transmission block 204 are airtightly connected with each other.
The force transmission block 204 is further connected to the top
surfaces of the mesa gauges 212, 214, 216, and 218, and the top
surface of the support 220. The semiconductor substrate 202 and the
force transmission block 204 are connected with each other by
cold-solid phase welding. More specifically, the main surface 202S
of the semiconductor substrate 202 and the surface of the silicon
oxide layer 204b of the force transmission block 204 are activated
by using argon ions. Thereafter, the main surface 202S of the
semiconductor substrate 202 and the surface of the silicon oxide
layer 204b of the force transmission block 204 are brought into
contact with each other in ultra-high vacuum to connect both the
surfaces.
As illustrated in FIG. 11, a part of the silicon oxide layer 204b
of the force transmission block 204 is removed to form a groove
204c on the surface of the force transmission block 204 on the
semiconductor substrate 202 side. The groove 204c is disposed in
such a position as to face an area between the mesa gauges 212,
214, 216, and 218 of the semiconductor substrate 202 and the
sealing portion 230. The groove 204c surrounds the entire
circumference of the mesa gauges 212, 214, 216, and 218 in the plan
view of the force detection apparatus 201. The groove 204c thus
formed defines a sealed space 206 between the semiconductor
substrate 202 and the force transmission block 204 as a space
separated from the outside.
Operation of the force detection apparatus 201 will be described.
Initially, the force detection apparatus 201 during the use is
brought into a state of connection between the first electrode 242
and a constant current source, grounding of the third electrode
246, and connection of a voltmeter between the second electrode 244
and the fourth electrode 248. According to the force detection
apparatus 201, compressive stress applied to the gauge portions
212a, 214a, 216a, and 218a of the mesa gauges 212, 214, 216, and
218 via the force transmission block 204 changes when a combustion
pressure applied to the force transmission block 204 changes.
Electric resistances of the gauge portions 212a and 216a change in
proportion to the compressive stress by a piezoresistance effect of
the gauge portions 212a and 216a. In this case, a potential
difference between the second electrode 244 and the fourth
electrode 248 becomes proportional to the compressive stress
applied to the gauge portions 212a and 216a. Accordingly, the
combustion pressure applied to the force transmission block 204 is
detectable based on a voltage change measured by the voltmeter.
As illustrated in FIG. 13, the sealed force detection apparatus 201
includes the sealed space 206 between the semiconductor substrate
202 and the force transmission block 204. The sealed space 206 is
separated from the outside by airtight connection between the
sealing portion 230 of the semiconductor substrate 202 and the
force transmission block 204. In this case, a pressure difference
between the internal air pressure of the sealed space 206 and the
combustion pressure increases as the combustion pressure increases
in the sealed force detection apparatus 201. Accordingly, force F2
corresponding to the sum of the combustion pressure applied to a
pressure receiving area of the force transmission block 204
(corresponding to the area between the mesa gauges 212, 214, 216,
and 218 and sealing portion 230 in the plan view of the force
detection apparatus 201) bends the force transmission block 204
toward the sealed space 206. This condition produces a leverage
relationship which defines the bended and deformed portion of the
force transmission block 204 as the point of power, the support 220
as the fulcrum, and the mesa gauge 212 as the point of action.
Assuming that the distance between the fulcrum of the support 220
and the point of action of the mesa gauge 212 is a distance L1, and
that the distance between the fulcrum of the support 220 and the
point of power of the deformed portion is a distance L2, force F1
applied to the point of action is expressed by the following
expression 1 under a condition producing an ideal leverage
effect.
.times..times..times..times. ##EQU00001##
As described above, the sealed force detection apparatus 201 in
this example is configured to exhibit a leverage relationship. In
this case, the force F2 applied to the force transmission block 204
is amplified into the force E1, and the force F1 is applied to the
mesa gauges 212 and 216 as amplified force. Accordingly, sensor
sensitivity of the force detection apparatus 201 considerably
improves.
For improving sensor sensitivity of the force detection apparatus
201 as expressed in Expression 1, it is preferable that the value
L2/L1 becomes large, more specifically, 2 or larger.
As illustrated in FIG. 14, both the silicon oxide layer 204b and
the silicon layer 204a may be processed to form the groove 204c
defining the sealed space 206. For producing a leverage effect, the
force transmission block 204 needs to bend at a position
corresponding to the sealed space 206. When the thickness of the
silicon layer 204a at the position corresponding to the sealed
space 206 is reduced as illustrated in FIG. 14, the corresponding
portion of the silicon layer 204a bends in a preferable condition.
Accordingly, a more preferable leverage effect is achievable.
As illustrated in FIG. 15, the main surface 202S of the
semiconductor substrate 202 may be processed to produce the groove
204c defining the sealed space 206. The groove 204c of this example
may be produced in the same step as the manufacturing step of the
mesa gauges 212, 214, 216, and 218, and the support 220 by dry
etching.
Each of the semiconductor substrates 2 and 202 corresponds to an
example of a substrate according to the present disclosure.
While specific examples of the present disclosure have been
explained in detail, they are just examples. It should be noted
that they does not limit embodiments, configuration, and modes
according to the present disclosure. Art relating the present
disclosure includes a thing obtained by modification or change of
the exemplified specific examples in various ways. Further,
technique elements explained in the description or the drawings
show a technical utility by alone or various combinations, and it
is not limited to a combination described in claims at the
application. Further, a technique exemplified in the present
description or the drawings may concurrently obtain multiple
purposes, and a technical utility is realized by achieving one of
the purposes itself.
* * * * *